Parallel XBAR Sub-Resonator Layout for Wider RF Filter Bandwidth
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Solution Overview
Problem
Current RF filters, particularly those using acoustic wave resonators, are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which includes bands n77, n79, and millimeter wave frequencies, leading to performance limitations in systems like mobile networks and Wi-Fi.
Innovation Solution
The development of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with multiple sub-resonators in parallel configurations, which utilize a piezoelectric diaphragm and interdigital transducers to achieve high electromechanical coupling and frequency capability, allowing for improved performance in high-frequency filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional acoustic wave resonators are used, then the filter structure is simple, but the frequency capability and bandwidth are limited for future communication networks
Solution Approach 1:
The resonator is divided into multiple sub-resonators connected in parallel between common nodes. Each sub-resonator has its own IDT and acoustic cavity, allowing independent optimization. This segmentation enables the filter to achieve higher frequency capability and wider bandwidth while maintaining a modular structure that is manageable in complexity.
2Strength
If a single resonator is used, then the device is compact, but the mechanical rigidity is insufficient leading to higher parasitic resistivity
Solution Approach 1:
Multiple sub-resonators are connected in parallel between common nodes, merging their mechanical and electrical properties. This parallel configuration increases the overall mechanical rigidity of the resonator system and reduces parasitic resistivity by providing multiple parallel current paths, thereby reducing energy loss.
3Adaptability or versatility
If multiple sub-resonators are added in parallel, then the bandwidth and frequency capability improve, but the device area increases
Solution Approach 1:
The patent utilizes vertical cavity structures and three-dimensional electrode interleaving to achieve multiple sub-resonators in a compact footprint. By transitioning from purely planar layouts to incorporating vertical dimensions and立体 structures, the filter achieves wider bandwidth through multiple parallel resonators without proportionally increasing the device area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The XBARs with sub-resonators in parallel configurations enhance the mechanical rigidity and reduce parasitic resistivity, leading to improved filter performance, including reduced insertion loss and increased bandwidth, effectively addressing the limitations of existing filters for future communication standards.
Implementation Method 1
The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Implementation Method 2
XBAR resonators provide very high electromechanical coupling and high frequency capability. XBAR resonators may be used in a variety of RF filters including band-reject filters, band-pass filters, duplexers, and multiplexers.
Data Source
AI summary
Acoustic filter devices and methods of making filter devices. An acoustic filter device includes a transversely-excited film bulk acoustic resonator (XBAR) including a plurality of sub-resonators and conductors to connect the plurality of sub-resonators in parallel between a first node and a second node. The conductors are configured such that a path length from the first node to the second node is effectively the same through each of the plurality of sub-resonators.